Fix crash when clicking on another object mid-placement of spinner

[bdach]

Closes #38509.

You might be thinking: "@bdach is dumb and/or incompetent for not just directly reverting #38464 and instead just reverting half of it in #38506". That is certainly what I was thinking until I tried reverting and found that it actually doesn't help. This is actually a silent regression from #37485!

The chain of failure goes something like this:

1. Start with editor seeked to a start time of one of the existing objects.

2. Begin placing a spinner.

3. Click the object that starts at the current time.

4. On master, SpinnerPlacementBlueprint does not consume the left click input when spinner placement has already started. This means that the left click input is allowed to fall through to the blueprint container.

5. When the left click input falls through to the blueprint container, it triggers selection logic to fire and the existing object to become selected.

6. Object selection changing also changes the currently used tool to the "select" tool:

   osu/osu.Game/Rulesets/Edit/HitObjectComposer.cs

   Lines 504 to 511 in cd27c93

   	private void selectionChanged(object sender, NotifyCollectionChangedEventArgs changedArgs)
   	{
   	if (EditorBeatmap.SelectedHitObjects.Any())
   	{
   	// ensure in selection mode if a selection is made.
   	SetSelectTool();
   	}
   	}

7. Changing the currently used tool causes any pending placement to be committed if valid:
   

   osu/osu.Game/Screens/Edit/Compose/Components/ComposeBlueprintContainer.cs

   Lines 437 to 438 in abbf6e2

   	// As per stable editor, when changing tools, we should forcefully commit any pending placement.
   	CommitIfPlacementActive();

8. Committing the placement causes the object whose attempt at selection triggered this entire chain of events to begin with to be removed:
   

   osu/osu.Game/Rulesets/Edit/HitObjectComposer.cs

   Lines 545 to 550 in cd27c93

   	EditorBeatmap.BeginChange();
   	foreach (var h in EditorBeatmap.HitObjects.Where(ho => blueprintContainer.CurrentHitObjectPlacement?.ReplacesExistingObject(ho) == true).ToArray())
   	EditorBeatmap.Remove(h);
   	EditorBeatmap.Add(hitObject);
   	EditorBeatmap.EndChange();

   And therefore the failure is understandable, because at that point the placement blueprint of the now-removed object really does not reside in the container.

   Prior to Replace hit objects when placing at same time in editor #37485 this would not cause an issue because the objects would both exist here.

To fix, prevent the issue at point (4) by making the placement blueprint consume left clicks and not allow fall-through to existing objects.

[peppy]

Confirm crash and confirm fix. Editor interactions are... complex.